Dating back to the 1930s, hydroponics is the science of growing plants in a liquid nutrient solution rather than in soil. The plants are supported in a sterile, inert medium, such as gravel or peat, and regularly flooded with a nutrient-rich solution, which is drained off and reused until it is no longer beneficial. The air and light in a hydroponic enclosure is strictly controlled to insure optimal production. Increased yields are further insured because hydroponically grown vegetables can be planted much closer together than those in the field. Yet another bonus is that hydroponic farmers are not besieged by weeds and pests, which means their crops are pesticide free. With the science of hydroponics, plants can be grown in areas where the climate is inhospitable or the soil is unsuitable. This means that perfect tomatoes can be grown in the desert or in the middle of winter. See also aquaculture.